1. Field of the Invention
This invention relates to an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, such as a copying apparatus or a laser beam printer, and in particular to cleaning of a corona discharging device used in such image forming apparatus.
2. Description of the Prior Art
In an image forming apparatus, in order to charge or discharge an image bearing member, use has heretofore been made of a corona discharging device for applying a high voltage to a wire having a diameter on the order of 0.1 mm to thereby create corona discharge.
However, in the corona discharging device, there has been a problem that the corona discharging wire functioning as a corona discharging electrode is liable to be stained by developer and other foreign substances, and this stain causes irregularity of discharge. This in turn has led to a disadvantage that when image formation is effected with the stained corona discharging wire, the irregularity of discharge clearly appears as an irregularity in the image. Accordingly, it has been necessary to always keep the corona discharging wire stainless and clean.
So, there have heretofore been devised various methods of cleaning the corona discharging wire.
For example, there is a method in which a cleaner for contacting the corona discharging wire is securely provided on the image forming apparatus body side and the corona discharging device itself is inserted and removed with respect to the apparatus body to thereby clean the wire (see Japanese Patent Publication No. 1830/1976). However, this method has suffered from an inconvenience that when other maintenance, such as the height adjustment of the wire, is to be effected on the corona discharging device, the corona discharging device cannot be pulled out unless the cleaner is removed from the apparatus body each time.
There is also known an apparatus in which the corona discharging device itself is provided with means for cleaning the corona discharging wire by the sliding of a rod or the like (U.S. Pat. No. 3,942,006), but such an apparatus has suffered from a disadvantage that generally the apparatus becomes complicated and bulky.
On the other hand, recently, image forming apparatuses designed such that process elements such as an image bearing member, a corona discharging device, a developing device and a cleaning device which are directly concerned with image formation and particularly require sufficient maintenance are contained in a cartridge and the cartridge is interchanged instead of effecting maintenance of the individual process elements, have become popular. However, in such apparatus, in order to achieve a reduction in cost and exclude uselessness with respect also to the method of fixing each process element, there is not provided, for example, a construction for inserting and removing the corona discharging device, etc., but there is adopted the simplest possible construction in which the corona discharging device is fixed to the frame member of the cartridge as by screws. Also, basically, the cartridge is designed such that its interior cannot be touched from outside and therefore, a contrivance is necessary in respect also of the cleaning of the corona discharging wire.
With regard to the cleaning of the corona discharging wire in such image forming apparatuses, there is a device as shown in assignee's, U.S. application Ser. No. 523,365 (filed on Aug. 15, 1983), now U.S. Pat. No. 4,566,777, wherein a slit opening is formed in the cartridge frame member on the back side of the corona discharging device and a separate cleaner is inserted through this opening to clean the corona discharging wire. However, this cleaner is devised as a supplemental means for an apparatus in which the copy volume per cartridge is 2,000 to 3,000 sheets and there is relatively little stain of the corona discharging wire. For a cartridge corresponding to an apparatus of greater copy volume, it becomes necessary to clean the corona discharging wire simply and reliably.